At the time of that statement in late October, Sprint had been offering the iPhone for only a short time, but as Hesse added in that same call, "We believe two weeks in the market is not enough time to constantly estimate expected gross-add percentages ... but early indications are extremely encouraging."

Below is a chart showing Sprint's 2011 stock price along with the percentage of its revenue growth. Note the precipitous drop in the blue revenue-growth line until it reaches the end of the third quarter. If, as CEO Hesse says, the iPhone will promote a turnaround in Sprint's customer and revenue growth, that blue line should follow a significant upward trajectory when the company's fourth quarter earnings are released.

The iPhone paradoxEstimates are that Sprint activated almost two million iPhones in the fourth quarter. That should be compared to the 7.6 million iPhones that AT&T (NYS: T) activated and the 4.2 million that Verizon (NYS: VZ) activated during that same period. The paradox here is that the greater revenue generated by iPhone sales is more than offset by the subsidies each carrier must pay on each phone to encourage subscribers to sign long-term contracts. So selling more iPhones may not be the road to immediate riches.

The 4G predicamentSprint's supplier of 4G services has been -- and still is -- Clearwire (NAS: CLWR) . Unfortunately for both companies, the flavor of 4G supplied by Clearwire is of the older and slower WiMAX type. Both of Sprint's much-larger rivals, Verizon and AT&T, offer the faster LTE 4G wireless broadband service. As smartphones proliferate, especially LTE-capable smartphones, the more urgent will be Sprint's need to get on the LTE train.

Looking forwardSo the main things to look for in Sprint's upcoming fourth-quarter earnings report boil down to what effect the iPhone has had on revenues and profit margins; and the company's 2012 LTE rollout projections. Stay tuned for the Fool's coverage of Sprint's earnings statement as soon as it comes out.

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